Self-Composite Comprised of Nanocrystalline Diamond and a Non-Diamond Component Useful for Thermoelectric Applications

ABSTRACT

One provides nanocrystalline diamond material that comprises a plurality of substantially ordered diamond crystallites that are sized no larger than about 10 nanometers. One then disposes a non-diamond component within the nanocrystalline diamond material. By one approach this non-diamond component comprises an electrical conductor that is formed at the grain boundaries that separate the diamond crystallites from one another. The resultant nanowire is then able to exhibit a desired increase with respect to its ability to conduct electricity while also preserving the thermal conductivity behavior of the nanocrystalline diamond material.

RELATED APPLICATIONS

This application is a continuation of and claims the benefit of U.S.patent application Ser. No. 12/860,405, filed on Aug. 20, 2010, which isa continuation-in-part of and claims benefit of U.S. patent applicationSer. No. 12/297,979 filed on Oct. 21, 2008 (as a Section 371 filingbased upon PCT/US07/67297 filed Apr. 24, 2007), which is a continuationof U.S. patent application Ser. No. 11/674,810 filed on Feb. 14, 2007,which is a continuation-in-part of U.S. patent application Ser. No.11/380,283, filed on Apr. 26, 2006, which claims benefit of 60/725,541,filed on Oct. 11, 2005, all of which are hereby incorporated herein byreference in their entirety.

GOVERNMENT RIGHTS

This invention was made with Government support under Contract No.W-31-109-ENG-38 awarded by the United States Department of Energy. TheGovernment has certain rights in this invention.

TECHNICAL FIELD

This invention relates generally to nanocrystalline diamonds.

BACKGROUND

The direct conversion of thermal energy into electrical energy (withoutthe use of rotating machinery) is known in the art. This technologytypically finds little practical application, however, as presentlyachievable conversion efficiencies are quite poor. For example, whilesuch mechanisms as steam turbines are capable of conversion efficienciesin excess of about 50%, typical prior art direct conversionthermoelectric energy (TE) techniques offer only about 5 to 10%conversion efficiencies with even the best of techniques yielding nomore than about 14% in this regard.

TE technologies generally seek to exploit the thermal energy ofelectrons and holes in a given TE material to facilitate the conversionof energy from heat to electricity. An expression to characterize themaximum efficiency for a TE power generator involves several termsincluding the important dimensionless figure of merit ZT. ZT is equal tothe square of the Seebeck coefficient as multiplied by the electricalconductivity of the TE material and the absolute temperature, as thendivided by the thermal conductivity of the TE material. With a ZT valueof about 4, a corresponding TE device might be expected to exhibit aconversion efficiency approaching that of an ideal heat-based engine.Typical excellent state of the art TE materials (such as Bi2Te3—Bi2Se3or Si—Ge alloys), however, have ZT values only near unity, therebyaccounting at least in part for the relatively poor performance of suchmaterials.

To reach a value such as 4 or higher, it appears to be necessary tomaximize the power factor while simultaneously minimizing the thermalconductivity of the TE material (where the power factor can berepresented as the product of the square of the Seebeck coefficient andthe electrical conductivity). This has proven, however, a seeminglyintractable challenge. This power factor and thermal conductivity aretransport quantities that are determined, along with other factors, bythe crystal and electronic structure of the TE material at issue. Theseproperties are also impacted by the scattering and coupling of chargecarriers with phonons. To maximize TE performance, these quantitiesseemingly need to be controlled separately from one another and this,unfortunately, has proven an extremely difficult challenge when workingwith conventional bulk materials.

Bulk diamond materials are also known in the art. As bulk diamondcomprises both an outstanding thermal conductor and a superb electricalinsulator, bulk diamond is quite unsuited for use as a TE material forat least the reasons set forth above. In more recent times, however,nanocrystalline diamond material (having crystallite sizes of about 2 to5 nanometers) has been successfully doped to achieve n or p-typeelectrically conducting material at ambient temperatures of interestwhile also exhibiting very low thermal conductivity. Thesecharacteristics of nanocrystalline diamond material suggest its possibleemployment as a useful TE material. To date, however, no one hassuggested a way to make good upon this possibility and hopes for auseful TE material continue to remain mere unmet aspirations.

BRIEF DESCRIPTION OF THE DRAWINGS

The above needs are at least partially met through provision of the anapparatus, method, and article of manufacture corresponding to aself-composite comprised of nanocrystalline diamond and a non-diamondcomponent described in the following detailed description, particularlywhen studied in conjunction with the drawings, wherein:

FIG. 1 comprises a flow diagram as configured in accordance with variousembodiments of the invention;

FIG. 2 comprises a schematic perspective view as configured inaccordance with various embodiments of the invention;

FIG. 3 comprises a schematic perspective view as configured inaccordance with various embodiments of the invention;

FIG. 4 comprises a flow diagram as configured in accordance with variousembodiments of the invention; and

FIG. 5 comprises a block diagram as configured in accordance withvarious embodiments of the invention.

Skilled artisans will appreciate that elements in the figures areillustrated for simplicity and clarity and have not necessarily beendrawn to scale. For example, the dimensions and/or relative positioningof some of the elements in the figures may be exaggerated relative toother elements to help to improve understanding of various embodimentsof the present invention. Also, common but well-understood elements thatare useful or necessary in a commercially feasible embodiment are oftennot depicted in order to facilitate a less obstructed view of thesevarious embodiments of the present invention. It will further beappreciated that certain actions and/or steps may be described ordepicted in a particular order of occurrence while those skilled in theart will understand that such specificity with respect to sequence isnot actually required. It will also be understood that the terms andexpressions used herein have the ordinary meaning as is accorded to suchterms and expressions with respect to their corresponding respectiveareas of inquiry and study except where specific meanings have otherwisebeen set forth herein.

DETAILED DESCRIPTION

Generally speaking, pursuant to these various embodiments, one providesnanocrystalline diamond material that comprises a plurality ofsubstantially ordered diamond crystallites that are each sized no largerthan about 10 nanometers. One then disposes a non-diamond componentwithin the nanocrystalline diamond material. By one approach thisnon-diamond component comprises an electrical conductor that is formedat the grain boundaries that separate the diamond crystallites from oneanother. The resultant nanowire is then able to exhibit a desiredincrease with respect to its ability to conduct electricity while alsopreserving the thermal conductivity behavior of the nanocrystallinediamond material.

The nanocrystalline diamond material may comprise, for example,nanocrystalline diamond film, bulk nanocrystalline diamond material, andso forth. The non-diamond component can comprise, for example, one ormore of disordered and defected carbon, defected graphite crystallitesthat are sized no larger than about 10 nanometers, and pristine ordefected carbon nanotubes.

By one approach the nanocrystalline diamond material can be doped toachieve n or p-type deposits that further enhance a desired level ofelectrical conductivity. This doping can be inhomogeneously achieved ifdesired. It is also possible, if desired, to achieve inhomogeneoussp2/sp3 distributions as pertains to the nanocrystalline diamond and thenon-diamond component.

So configured, these teachings appear able to yield appreciablequantities of a self-assembled, self-ordered material having propertieswell suited to TE power generation. It appears reasonable, for example,to expect such materials to exhibit a level of conversion efficiencythat compares well against existing non-TE approaches. This, in turn,presents the possibility and hope of providing improved TE powergenerators not only in situations where TE generation is already usedbut as a substitute for existing rotating-machinery-based powergeneration.

These and other benefits may become clearer upon making a thoroughreview and study of the following detailed description. Referring now tothe drawings, and in particular to FIG. 1, an illustrative correspondingprocess 100 begins with provision 101 of nanocrystalline diamondmaterial comprising a plurality of substantially ordered (and preferablyself-assembled) diamond crystallite particles each sized no larger thanabout 10 nanometers. This material might also comprise occasionallarger-sized particles, of course, but should nevertheless besubstantially if not exclusively comprised of particles of about 1 to 10nanometers in size.

By one approach this nanocrystalline diamond material can comprisenanocrystalline diamond film. By another approach this nanocrystallinediamond material can comprise bulk nanocrystalline diamond material.Further description regarding both of these approaches will be providedfurther below.

This process 100 then provides for disposing 102 a non-diamond componentwithin the nanocrystalline diamond material. By one approach thisnon-diamond component comprises at least one of disordered and defectedcarbon, defected graphite crystallites each sized no larger than about10 nanometers, and/or at least singly-walled (or multi-walled) pristineor defected carbon nanotubes. There are various ways by which this stepcan be carried out as well and further details in this regard are alsoset forth further below.

By one approach these teachings can be employed to yield superlatticenanowires (having a width, for example, of no greater than about 40nanometers and an aspect ration exceeding ten to one or even 100 to one)comprised of such materials. As will be illustrated below, each suchnanowire can itself be comprised of nanocrystalline diamond thatpresents itself as helically arranged diamond nanocubes with theaforementioned non-diamond component being disposed between the grainboundaries of such diamond nanocubes.

As mentioned above, the nanocrystalline diamond can comprise ananocrystalline diamond film. By one approach, the above-mentionednon-diamond component in the form of single-wall and/or multi-wallcarbon nanotubes are conformally coated with n or p-type nanocrystallinediamond. As noted above, the formation of n or p-type nanocrystallinediamond is known in the art. By one approach, an Astex PDS 17 vapordeposition machine serves to generate a microwave plasma in a gas thatcomprises about 1% C60 or other hydrocarbon of interest (such as CH4)and 99% argon to which either nitrogen (for n-type doping) ortrimethylboron (for p-type doping) has been added. A small amount ofoxygen containing species can also be introduced, if desired, to aidwith reducing soot formation.

To illustrate further, nanocrystalline diamond having n-type depositscan be prepared using a mixture of argon, nitrogen (about 20% byvolume), and CH4. The nitrogen content in the synthesis gas produceshighly aligned, oriented, and textured nanocrystalline diamondformations on the carbon nanotubes. Resultant electrical conductivitycan be increased by using and controlling high temperature annealing ina vacuum furnace where the latter serves to graphitize the disorderedcarbon at the grain boundaries of the nanocrystalline diamond grains andto induce transformation of three layers of (111) nanocrystallinediamond into two (002) graphitic layers. Both graphitic layers result inthe introduction of narrow electronic peaks near or at the Fermi levelinto the density of states. If desired, by establishing a temperaturegradient in the vacuum furnace, inhomogeneous graphitization can beinduced.

The useful orientation imposed on the nanocrystalline diamond by thenitrogen is due, it is believed, to changes in the alpha parameter(i.e., the ratio of growth velocities of different diamond crystaldirections). Relatively high growth temperatures as employed pursuant tothese teachings strongly enhance texture that results in a profoundconformational transformation that may be characterized as a helixcomprised of nanocrystalline diamond crystallites possessing a cubichabit. By increasing the growth temperature by about 300 degreescentigrade (as compared to a prior art value of about 800 degreescentigrade) the alpha parameter is decreased from a more typical valuethat is larger than unity to a value that is essentially equal to unity.This, in turn, tends to lead to a crystal habit that is a perfect cubewhich in turn facilitates the self-assembling self-ordering creation ofthe previously mentioned helix configuration.

Referring to FIG. 2, an exemplary illustrative nanowire 201 may comprisea single helix of diamond nanocubes 201 having the aforementionednon-diamond components at the grain boundaries 203 between such diamondnanocubes. Those skilled in the art will appreciate that the nanowire201 depicted has a length that is shown arbitrarily short for the sakeof illustrative clarity. In an actual embodiment this nanowire 201,though perhaps only 10 to 20 nanometers in width, can be hundreds (oreven thousands) of nanometers in length. Those skilled in the art willfurther recognize and appreciate that such ordering is quite theopposite of the random orientation that one typically associates withprior art nanocrystalline diamond procedures and materials. It isbelieved that, at least in theory, this ordered construction shouldaccount for a 10× or better improvement with respect to electricalconductivity as compared to a non-ordered construction.

Those skilled in the art will further understand and appreciate thateach diamond nanocube 202 comprises a lattice structure. Accordingly,when these nanocubes 202 self-order themselves in the ordered helicalstructure shown, the resultant ordered and arranged structure canproperly be viewed as a superlattice nanowire.

With reference now to FIG. 3, it is also possible for these teachings toresult in the self-assembly and self-ordering of diamond nanocubes as adouble helix nanowire 301 where, again, non-diamond components such asdisordered and defected carbon, defected graphite crystallites, and/orcarbon nanotubes are disposed at the grain boundaries of these diamondnanocubes.

It is believed that post-growth relatively high temperature annealingfurther aids to bring about the above-described carbon structures and inparticular a second helix of graphitic or otherwise conductive nanowiresthat are covalently bonded to the helix of nanocrystalline diamondmaterial. Those skilled in the art will appreciate that a relativelywide range exists for the manipulation of electronic structures such asp-n junctions as both the nanocrystalline diamond and the non-diamondcomponent helices can be separately and independently formed with n orp-type deposits. As both the helices and the nanotubes are covalentlybonded to each other, efficient electron transport between these helicesand nanotubes is easily facilitated.

A transition metal catalyst such as ferrocene or iron trichloride can becontinuously added throughout the synthesis process. This so-calledfloating catalyst methodology aids with ensuring that simultaneousgrowth of the nanocrystalline diamond and of the carbon nanotubes occursthroughout the resultant thick film(s). The ratio of nanocrystallinediamond to carbon nanotubes can be at least partially controlled byadjusting the catalyst-to-carbon ratio. The latter may be accomplished,for example, by controlling the rate and/or quantity of catalystintroduced into the process.

By one approach, the Astex PDS 17 machine is modified to include aferrocene transpiration apparatus comprising a tube having segmented,differentially heated zones that allow the establishment of atemperature gradient between the catalyst bed and the Astex PDS 17reaction chamber. Adjustment of the temperature in this way produceslocally useful ferrocene vapor pressures.

A small positive bias of a few volts can be applied to the substrateduring growth to facilitate the extraction of negatively charged C2species from the aforementioned plasma. Such components will react withthe carbon nanotubes to effect alteration of the electronic structure ofthe latter. The magnitude of the bias can be controlled to therebyselect for specific structural carbon nanotube alterations via thisreaction.

By one approach n-type nanocrystalline diamond can be formed usingN2/Ar/PH3/CH4 mixtures. This approach will place phosphorous in thenanocubes and also in the grain boundaries themselves with a givencorresponding distribution ratio between these two points of reference.Phosphorus in the grain boundaries will tend to enhance the formation ofpi-bonded carbon (much like nitrogen) and will also promote (111)texturing. In addition, p doping of the diamond nanocubes will occurprimarily due to boron substitution for carbon in the diamond material.

The presence of phosphorous in the diamond nanocubes and in the grainboundaries will simultaneously provide two different mechanisms forenhancing the density of states at the Fermi level, thus increasing theSeebeck coefficient for this material. In particular, in the grainboundaries, pi-bonded disordered carbon due to the presence of thephosphorous gives rise to a new electronic state. In addition,substitutional phosphorous in the diamond nanocubes themselvesintroduces a doping level situated about 0.6 ev below the diamondconduction bands. This level introduces new electronic states andcontributes to conductivity particularly at the higher temperaturesenvisioned for thermoelectric application of these materials.

By one approach p-type nanocrystalline diamond can be formed usingAR/B2H6/CH4 or Ar/B2H6/CH4/N2 mixtures using plasma enhanced chemicalvapor deposition techniques as are known in the art. Using this approachboron will be situated in both the diamond nanocubes and in the grainboundaries themselves. Concentrations between these two locations willagain be determined by a corresponding distribution coefficient. Whenboth N2 and B are present, compensation between n and p-type behavior inthe grain boundaries will tend to occur. The behavior of B dopednanocrystalline diamond will be largely equivalent to that of p dopednanocrystalline diamond in that both will behave as semiconductors orsemimetals depending on the concentration of the dopant.

Boron doping of nanocrystalline diamond introduces states near the Fermilevel. As a result, the simultaneous presence of states near the Fermilevel as introduced by defects in the carbon grain boundaries (or, forexample, in graphitic nanowires when present) provides a powerfulmethodology for manipulating the states that control the magnitude ofthe Seebeck coefficient in ways not available by any other knownmaterials system. Much the same occurs when considering theaforementioned n doped nanocrystalline diamond.

So configured, the electrically conducting but thermally insulatingconformal coating of nanocrystalline diamond on the non-diamondcomponent also presents high carrier concentrations of 10+19 to 10+20per cubic centimeter. Being covalently bonded to, for example, a carbonnanotube-underpinning, the nanocrystalline diamond injects carriers intothe carbon nanotubes which, upon reaching the end of a particular carbonnanotube, returns to the nanocrystalline diamond which then transportsthose carriers to the next carbon nanotube in the thick film deposit. Anapt analogy might be a relay race being run by alternatively fast andslow runners with the baton comprising an electron that is movingthrough a thermal gradient as is imposed on this material.

As mentioned above, the nanocrystalline diamond material can alsocomprise bulk nanocrystalline material if desired. For example,ultradispersed diamond crystallites (as may be formed, for example,using detonation techniques) are commercially available in bulk formhaving particles sized from about 2 to 10 nanometers. More particularly,coupons are available that are comprised of ultradispersed diamondcrystallites and single-wall or multi-wall carbon nanotubes.

With this in mind, and referring now to FIG. 4, a corresponding process400 begins with providing 401 such a composite material and thenexposing the carbon nanotubes to a mass and energy selected beam ofnegatively charged C2 molecules. This may comprise use, for example, ofeither photofragmentation or electron bombardment of C60 in order toproduce the desired states at the Fermi level that are responsible forthe desired high resultant Seebeck coefficients.

As a next step, this process 400 reacts 403 both the nanocrystallinediamond material and the carbon nanotubes in appropriate amounts withone or more monomers. Depending upon the monomer employed, the monomerwill react with the composite material to produce n or p-type deposits.For example, when the monomer comprises an organic azide that attachescovalently at a nitrogen site n-type deposits will result. As anotherexample, when the monomer comprises an organoboron monomer (inparticular, an organoboron monomer that is capable of forming conductingfunctionalized polyacetylenes such as, but not limited to,mesitylborane, 9-borabicyclo[3.3.1]noane, and the like) that attaches ata boron site p-type deposits will result. By one approach, ultrasonictechniques are employed to facilitate coating substantially eachnanocrystalline diamond and carbon nanotube with the monomer of choice.

This process 400 then provides for converting 404 the monomer(s) to anelectrically conductive polymer such that the composite material is nowsubstantially coated with the resultant polymer. Such polymerization canbe achieved, for example, via pulsed plasma chemical methods or by useof other traditional catalyzed chemical reactions. By one approach, theresultant polymer comprises a functionalized polyacetylene.

As a next step one processes 405 the composite material and polymercoating to form the aforementioned non-diamond component. By oneapproach this comprises heating the composite/polymer material at highpressures to decompose the organic constituents and to induce incipientsintering. This procedure will lead to the formation of the previouslydescribed electrically conducting grain boundaries between the diamondcrystallites that conformally coat the carbon nanotubes.

It would also be possible to initially provide a nanocrystalline diamondmaterial that already includes n or p-type deposits. For example, boronor phosphorous can be added when forming such material using detonationtechniques. A conducting compact is made by reacting the dopednanocrystalline diamond power with a C2 containing microwave plasma. Theelectrical conductivity can be further enhanced by partialgraphitization of the compact at high temperatures.

As another approach, n or p-type nanocrystalline diamond can be preparedby mixing nanocrystalline diamond powder with nitrogen, boron, orphosphorous containing monomer molecules that are subsequentlypolymerized (with 5 to 10% of the total volume of the composite resultbeing the resultant polymer). This polymer will act as a matrix toprovide mechanical rigidity to a sheet that is then heated about 800degrees centigrade while being exposed to a C2 containing microwaveplasma. The C2 will react with the pyrolyzed polymer which in turnbecomes a grain boundary bonding the nanocrystalline diamond particlesinto an n or p-type compact. Electrical conductivity can then be furtherenhanced by use of post plasma high temperature processing.

So configured, and referring now to FIG. 5, such material can be readilyapplied as a key TE component. To illustrate, an n-type block 501 ofmaterial and a p-type block 502 of material as described above, whensubjected to a temperature gradient 503, will provide a voltagepotential 504 (as electrons will seek to flow from the warmer area tothe cooler area) at corresponding electrodes as shown to thereby providean effective and efficient TE power generator 500.

In some cases these teachings may further accommodate post-synthesisprocessing that serves to establish inhomogeneous sp2/sp3 distributionsof segmented nanocrystalline diamond/nanographitic nanowires. Suchstructures have been shown theoretically likely to provide conditionsunder which these nanomaterials can function as reversiblethermoelectric materials and reach considerably improved figures ofmerit and conversion efficiency. This inhomogeneous sp2/sp3 distributioncan be caused, for example, by imposing a temperature gradient asdescribed above in the vacuum furnace.

Those skilled in the art will recognize that a wide variety ofmodifications, alterations, and combinations can be made with respect tothe above described embodiments without departing from the spirit andscope of the invention, and that such modifications, alterations, andcombinations are to be viewed as being within the ambit of the inventiveconcept. To illustrate, n and p-type nanocrystalline diamond can also beprepared by adding elements such as sulfur, lithium, aluminum, and soforth. Such dopants can substitute for carbon in volumetrically expandedgrain boundaries (with those skilled in the art recognizing that suchdopants will likely not be suitable substitutes in the diamond latticeitself). These possibilities exist in large part owing to theopportunity presented by the volumetrically expanded ubiquitous grainboundaries that tend to characterize at least certain of theseteachings.

As another illustrative example in this regard, the above-describedsuperlattice nanowires can be obtained separate from the substrate onwhich they are formed by dissolution of the substrate. These nanowirescan be separated from the supernatant by filtration or centrifugation.The separated diamond nanowires can then be reacted with nanotubes toproduce TE materials. Those skilled in the art will appreciate, however,that many other uses are also possible such as electron emitters forflat panel displays or for thermionics. In biological applications,after surface derivatization, biological molecules (such as, but notlimited to, DNA, enzymes, and so forth) can be attached to thenano-diamond rods. These biologically active nano-diamond rods can thenbe injected, for example, into biological tissue for purposes of drugdelivery, biological sensing, and so forth.

As yet one more illustrative example in this regard, nanocrystallinediamonds and carbon nanotube composites can be formed by thermalprocessing of appropriately functionalized dispersed nanocrystallinediamonds and carbon nanotubes such as (but not limited to) a mixture ofhydrogen terminated dispersed nanocrystalline diamond and hydroxylatedcarbon nanotubes.

1. A method comprising: providing nanocrystalline carbon-containingsp3-bonded solid refractory material in the absence of a film andcomprising a plurality of crystallites each sized no larger than about10 nanometers; forming covalent bonds between a non-diamond componentand the nanocrystalline carbon-containing sp3-bonded solid refractorymaterial wherein the non-diamond component comprises at least one of:disordered carbon; and graphite crystallites each sized no larger thanabout 10 nanometers; and adding at least one non-carbon material tovolumetrically expanded grain boundaries as pertain to the crystallites.2. The method of claim 1 wherein the non-carbon material comprises anon-metal.
 3. The method of claim 2 wherein the non-metal materialcomprises sulfur.
 4. The method of claim 1 wherein the non-carbonmaterial comprises a metal material.
 5. The method of claim 4 whereinthe metal material comprises aluminum.
 6. The method of claim 1 whereinthe non-carbon material comprises an alkali-metal material.
 7. Themethod of claim 6 wherein the alkali-metal material comprises lithium.8. The method of claim 1 wherein the non-carbon material comprises atleast one of: sulfur; aluminum; lithium.
 9. The method of claim 1wherein forming the covalent bonds comprises forming athermoelectrically active material.
 10. The method of claim 9 furthercomprising: using the thermoelectrically active material to generateelectricity by subjecting the thermoelectrically active material to atemperature gradient to thereby provide a corresponding voltagepotential.